Ramakrishna Aluru - University of St Andrews

Ramakrishna Aluru
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Real Space Imaging of Magnetic Order in Fe1+yTe
In correlated electron materials, superconductivity and magnetic order often occur in close proximity
- small changes of doping, pressure or chemical composition can turn a material magnetically
ordered or superconducting. Understanding the relation between the two is believed to be key for
understanding the physics of unconventional superconductivity in these materials. Among the parent
compounds of the iron-based superconductors, the magnetic structure of FeTe is unique -- not only
is it rotated by 45° with respect to the magnetic structure found in the iron-pnictide materials, it is
also not connected to a nesting vector between different sheets of the Fermi surface. At increased
excess iron concentrations y, the magnetic structure becomes incommensurate.
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Here, we report real space imaging of the magnetic structure in Fe1+yTe by low temperature scanning
tunneling microscopy. Our data confirm that in the monoclinic phase, the modulation is truly
unidirectional, separated in different domains, whereas at higher excess iron concentration y>0.12,
in the orthorhombic phase, a transition to a phase with coexistence of stripes in both directions within
a single domain is observed, locally reminiscent of a plaquette order. Temperature dependent
measurements show that the magnetic contrast disappears on the scale of the magnetostructural
phase transition found in the bulk. We demonstrate preparation of ferromagnetic and antiferromagnetic tips on FeTe. Our results highlight the applicability of spin-polarized STM to study
magnetic order in strongly correlated electron materials.